Coaxial heat exchange apparatus with spacers



United States Patent [72] lnventor Winton A. Ticknor Lancaster, Ohio [21} Appl. No. 791,271 [22] Filed Jan. 15,1969 [451 Patented Dec. 15, 1970 [73] Assignee Owens-Corning Fiberglas Corporation a corporation of Delaware [54] COAXIAL HEAT EXCHANGE APPARATUS WITH SPACERS 10 Claims, 6 Drawing Figs.

[52] U.S.C| 165/81, 165/83, 165/154; 263/20 [51] Int. Cl F231 15/04 [50] Field of Search 165/83, 154. 81, 82: 263/20 [56] References Cited UNITED STATES PATENTS 1,941,258 12/1933 Gordon 122/510X 2,267,839 12/1941 Rehm 122/510 Primary Examiner-Albert W. Davis, Jr. A!!orneys-Staelin & Overman and Myron E. Click ABSTRACT: An embodiment disclosed herein illustrates a recuperator having an inner tube and means forming an air passage around the inner tube. Means are provided for maintaining a predetermined spacing between the passage-forming means and the inner tube which include a first element extending into the passage from one of the passage-forming means and inner tube and having a hook means formed thereon, and a second element extending into the passage from the other of said passage-forming means and inner tube and having an opening formed therein to receive and restrain or limit movement of the hook means.

COAXIAL HEAT EXCHANGE APPARATUS WITH SPACERS This invention relates to heat exchangers in general and is particularly applicable to recuperators in which hot gases such as hot products of combustion or flue gases are used to preheat air or fluid fuel to be used in combustion.

For convenience, the invention will be discussed in connection with recuperators associated with heating furnaces such as those used in the glass industry, in which flue or exhaust gas is used to preheat combustion air for the furnace burners, although it will be apparent that the inventionwill have other uses and provide advantages in other fields.

In glass industry heating furnaces, it is necessary to burn substantial amounts of fuel with large volumes of air in order to achieve high temperatures and large quantities of heat required for glass melting operations. Thisresults in large volumes of waste or flue gases, having high temperatures and heat content remaining after the primary heating use. These factors have long made it advantageous to use recuperatols or regenerators to recover some of the heat of the waste gases by using the hot flue gases to preheat the combustion air and thus increase the output of the furnace for a given amount of fuel consumption.

In recent years the greatly increased costs of fuel, labor and capital equipment and the attendant necessity for close cost control in all glass making operations, have made it important to recover as much heat as possible from flue gases and transfer it to the incoming combustion air in order to increase the heating efficiency and thus the output of the furnace to the greatest extent possible. It is also important that furnace shutdowns for maintenance, such as repair or replacement of recuperators, be reduced to a minimum. While new furnace installations are designed and built with these factors in mind, great efforts are also being made to increase the efficiencies and outputs of existing furnaces because of the high cost of new furnaces and long times required to build and put them into operation.

For these reasons it is desired that recuperators employed not only provide a high recovery of heat from flue gases, but also have long service lives with a minimum of maintenance and furnace shutdown, and further permit a reliable and constant heat exchange to be effected. This, however, is exceedingly difficult to achieve because of the extremely rigorous service conditions to which the recuperator heat exchange elements are subjected in operation.

In recuperators of the general type in connection with which this invention provides particular advantages, i.e. metallic recuperators, the heat exchange elements are exposed to hot waste or flue gases which often are of such high temperatures that they may be incandescent, and which usually have high velocities. The high temperatures alone have deteriorating effects on the metal of the walls of the heat exchange elements, and the relatively high velocities of the hot gases also tend to harmfully affect the metal by erosion. The flue gases usually also contain constituents which tend to corrode, erode or cause other deleterious chemical or metallurgical reactions on such metal, and this action is promoted by the high gas temperatures and velocities. In the heat exchange element these harmful efi'ects occur to the greatest extent on the portion of the heat exchange element initially facing or exposed to the flow of hot flue gas.

Other problems may occur because of distortions or warping of the recuperator heat exchange elements in which the inner and outer tubes of circular cross section define between them an annular space or passage which is clear except for spaced lugs intended to separate the tubes.

In such a recuperator heat exchange apparatus, one such distortion occurs when the portions of the wall facing the hot stream of flue gases distorts due to unequal expansion of the metal. When this occurs, there may be a corresponding decrease in the width of the annular space or passage between the inner and outer tubes in this area, thus restricting the amount of air which can flow in the hottest portion of the periphery of the heat exchange element.

In another distortion in this type of recuperator heat exchange apparatus, the outer tube or the tube not directly exposed to the hot flue gases may not expand as much as the tube so facing the gases. This distortion may also result in restriction of airflow. Both of the above types of distortions may occur together. Such distortions and the resulting reduction of airflow tend to cause additional increases in the heating of the portions of the tube wall facing the stream of hot gas, which heating causes additional distortion of the wall and further restriction of the airflow between the inner and outer tubes, and so on, frequently continuing until the tube facing the hot flue gases fails, as by a buckling inwardly. Such distortions thus may cause failure of the heat exchange elements of the recuperator or require frequent preventative inspection or repair. In either case the result is costly shutdowns and loss of production. v

In these structures stress caused by differential expansion of various parts may also be a major cause of failure, and any but minor repairs to the recuperator necessitates complete disassembly of the device and of any refractory brick work associated therewith.

It is, therefore, an object of this invention to provide an improved heat exchange apparatus.

It is a further object of this invention to provide an improved recuperator for heat exchange between hot flue gases and combustion air to be supplied to burners in a furnace.

It is a still further object of this invention to provide a heat exchange element in which two structural members are supported in a unitary fashion in spaced relation while permitting a different expansion and contraction rate for the two structural members.

In carrying out the above objects, the invention features in a preferred embodiment a recuperator comprising an inner tube, an outer tube surrounding the inner tube and defining a passage therebetween, and means for maintaining the inner and outer tubes in a predetermined spaced relationship. The spacing means preferably comprises a plurality of hook elements attached to one of the inner and outer tubes and extending toward the other of the tubes in the passage, and a like plurality of associated hook-receiving elements attached to the other of said tubes. Each of the hook-receiving elements has an opening formed therein to receive and restrain or limit movement of a corresponding hook element in a direction transverse to the passageway.

The corresponding hook-receiving elements may be advantageously arranged in a plurality of rows,-each row extending around an annular passageway. One or more of the hook elements in a first of the rows may open in a first direction while one or more hook elements in a second of the rows advantageously opens in a second or opposite direction to prevent disengagement of the hook elements from their corresponding receiving elements.

The plurality of rows may be divided into a plurality of zones. The dimensions of the hook and hook-receiving elements in a first zone may be varied from the dimensions of the hook and hook-receiving elements in a second zone to accommodate the varying or different amounts of expansion and contraction that may occur in the first and second zones. The hook and hook-receiving elements in each row are preferably positioned in a staggered relationship around the passage with respect to the hook and hook-receiving elements in adjacent rows to provide a more evenly distributed support relationship between the inner and outer tubes.

The opening formed in each of the hook-receiving elements may be formed sufficiently larger than a hook means received therein to permit a sliding engagement in a direction transverse to the passage to accommodate the difference in outward expansion and inward contraction of the inner and outer tubes. The opening in a hook-receiving element may be elongated in one or more directions in order to permit sliding engagement in more than one direction in the event that the difference in expansion and contraction of the inner and outer tubes causes the tubes to move in more than one direction with respect to each other.

In the embodiment illustrated herein the hook elements are shown as elongate bars having a flange extending vertically "therefrom. The elongate bars may be attached to the inner 'tube as shown in the drawing or attached to the outer tube. If the hot flue gases are flowing through the inner tube then it is advantageous to attach the elongate bar portion of the hook element to the inner tube. The inner tube has a tendency to buckle inwardly in some recuperator constructions and will thus more support or reinforcement will be provided by the elongate bar portion. The hook-receiving elements as shown in the drawing are substantially U-shaped brackets attached to the outer tube, although their attachment to the inner tube to receive hook elements attached to the outer tube may be effected if so desired.

" While the configuration of the hook elements and hookvreceiving elements shown has been found to be particularly advantageous, these configurations are not meant to be limiting. For example, in order to provide the support desired (against buckling of the inner tube it is not necessary that the hook-receiving element have a completely enclosed opening.

-That is, a hook-receiving element may be formed in the same shape as a hook element and disposed along one tube in a position to engage a hook element supported from the other tube.

The passage between the inner and outer tube may be closed at one end by a transverse partition joining the tubes to form in cooperation with the hook and hook-receiving elements a substantially unitary structure. The passage between Other objects, advantages and features of this invention will 1 become apparent from the description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical section through the axis of a recuperator embodying the teachings of this invention;

FIG. 2 is a side elevational view of an inner shell of the recuperator illustrated in FIG. 1;

FIG. 3 is a side elevational view of an outer shell of the recuperator illustrated in FIG. I;

FIG. 4 is an enlarged side elevational view of a hook ele- "ment and hook-receiving element embodying the teachings of this invention;

FIG. 5 is a plan view of the elements illustrated in FIG. 4;

. and

FIG. 6 illustrates an alternate configuration of spacing ele- 'ments embodying the teachings of this invention.

Referring now to the drawings there is illustrated in FIG. 1 a recuperator which comprises an inner tube or shell 10 and an outer tube or shell 12, which may be constructed from steel or other suitable metals. A metal expansion bellows 14 is welded to the outer tube 12 through a reinforcing band 16 and to the top of an inlet chamber l8 by another band 17. An outlet chamber 20 including a transverse partition ll closes the passage between and joins the tubes 10, 12 at one end. The walls of the inlet chamber 18 and the expansion bellows l4 combine to connect the other ends of the tubes l0, 12 to provide a unitary structure.

Since the inner tube It) and the outer tube 112 are at different temperatures during operation because of their expo- ;sure to gases of different temperatures they will expand at different rates and for different total distances. A space I3 is provided in the insulating side wall 46 to accommodate expansion 'of the outer tube 12 and insulation 46. The bellows 14 operates in a manner well known in the art to accommodate the greater axial expansion of the inner tube 10 over that of the outer tube 12 while still maintaining the inlet chamber, outlet chamber and the interconnecting heat exchange passage of the recuperator sealed.

The inlet chamber 18, receives combustion air for heating via an inlet connection 22 connected to a forced draft blower 24 by a conduit 28. The outlet chamber 20 is connected by means not shown to supply combustion air to the burners in the furnace. The chambers 18 and 20 are constructed to surround each end of the tubes 10 and 12 to act as constant pressure chambers for the supply and release of air after it has been heated by the combustion gases passing in heat exchange relationship with the inner tube It The hot flue gases escaping through the interior of the tube 10 heat the inner surface of the tube 10 causing heat to radiate from the outer surface of the tube 10 to air flowing through the annular passage formed between the outer tube 12 and the inner tube 10.

In order to overcome the problems set forth, hereinbefore, a plurality of rows of spacing means generally indicated at 50 are provided for maintaining the inner shell 10 within a predetermined range of distance from the outer shell 12 to prevent buckling of the inner shell inwardly and to prevent a restriction of the annular passage formed between the two shells.

Referring to FIGS. 4 and 5 there is illustrated in enlarged detail the spacer means 50 which includes a hook element 51 and a hook-receiving element 52. In the embodiments illustrated in FIGS. 4 and 5 the hook element 51 comprises an elongate bar portion 51a having a flange projection 51b extending vertically therefrom. The hook-receiving element 52 comprises a U-shaped bracket. The elements are attached to the inner and outer shells, respectively, preferably by welding.

The dimensions of the projecting flange 51b are such that a limited sliding engagement is permitted between the opening 52a and the flange 51b to permit the inner and outer tubes 10, 12 to expand or contract at different rates yet maintain the passage formed therebetween within a predetermined range of sizes desired for the passage of combustion air therethrough. It will be noted that expansion and contraction in the embodiment illustrated in FIGS. 4 and 5 is permitted not only transverse of the passage, or movement of the tubes 10 and 12 toward and away from each other, but also for differential ex pansion which may take place within one of the tubes alone. Movement is permitted for a limited distance in a side direction or laterally with respect to the passage. In addition,

movement is permitted in the third or axial direction when dif-- ferent expansion rates cause the inner shell ll) to expand upwardly or axially more than the outer shell 12. Thus, a limited range of movement has been provided by spacing means 50,

for one shell with respect to the other, in any one of or all three of the directions in which differential rates of expansion may occur.

Referring to FIG. 6 there is illustrated another embodiment of a spacing means 500 including a hook element 51 formed in the same manner as that illustrated in FIGS. 4 and 5, and a hook-receiving element 53 which may be formed simply as another book element which cooperates with the hook element 51 to maintain the spacing desired. This arrangement permits an accommodation of three-dimensional differences in expansion and contraction rates of the two structural wall members, and yet does not have a completely enclosed opening as that afforded by the U-bracket 52 in FIGS. 4 and 5. In

some instances the elongate bar section of a hook element 53 may afford a reinforcing of the outer tube 12. Since the opening formed in the hook-receiving element 53 is open on one side the difficulties in registering a hook element and hookreceiving element may be reduced during assembly of the. recuperator in certain instances.

Referring to FIG. 2 the location of the hook elements 51 is illustrated. The hook elements 51 are advantageously attached to the exterior of the inner tube 10 and arranged in rows around the circumference thereof. Each hook element 51 in each row may be located in a staggered position with respect to the hook elements in adjacent rows so that a more evenly distributed support relationship between the inner and outer tubes is provided.

The plurality of rows may be divided into a plurality of zones as shown in FIG. 2. The dimensions of one of the hook and hook-receiving elements in one zone may be varied'from' the dimensions of one of the hook and hook-receiving'ele ments in another zone to accommodate the varying or different amounts of expansion and contraction between the first and second zones. For example, in Zone 1 the elongate bar portion of the hook elements 51 may extend outwardly from the inner tube a predetermined distance. The elongate bar portion of hook elements in Zone 2 may extend outwardly from the inner tube 10 a farther distance than that chosen for the hook elements in Zone 1, since there is a greater expansion of the outer tube 12 in Zone 2 because the initially relatively cool combustion air flowing in Zone 1 has absorbed heat from Zone 1. Similarly, in Zone 3 the elongate bar portion of hook elements 51 may extend even farther from the outer surface of the inner tube 10 since the combustion air in Zone 3 is even warmer than it was in Zone 2. While the dimension in this instance being varied is the outward extension of the hook elements 51, it will be appreciated that other dimensions of either the hook element 51 or the hook-receiving element 52 may be varied to accommodate the different expansion and contraction rates in different zones or areas of the recuperator.

ln effect, the height dimension of the elongate bar portions 51a of the hook elements 51 limit the amount of travel of the shells toward each other and maintains a predetermined minimum spacing or distance between the shells.

The spacing of the inner side of the flange projections 51b from the inner shell, in cooperation with the dimensions of the slot or opening formed in the hook-receiving element 52, limits the amount of travel of the shells away from each other and maintains a maximum spacing between the shells.

The above dimensions may be varied to determine maximum and minimum spacings, before and after expansion or contraction, between different zones to control passage size in response to temperature changes, to prevent buckling away from each other, and to enable a regulated heat exchange.

it will be noted in F IG. 2 that the hook elements in the third zone open downwardly while the hook elements in the first and second zones open upwardly. After assembly of the inner and outer shells, as will be described hereinafter, has been completed the opening of hook elements in opposite directions prevents the hook elements and hook-receiving elements from becoming disengaged and failing to perform their function. Accordingly, the joining of the inner and outer tubes at the upper and lower ends thereof provides a unitary structure through the expansion bellows which permits contraction and expansion along the vertical length 'of. the recuperator. The engagement of the hook elements and the hook-receiving elements as just described also provides a unitary structure effect between the inner and outer tubes to prevent a collapse of the inner tube or a restriction of the passage between the inner and outer tubes.

Thus, a complete unitary structure has been provided which permits expansion and contraction in three directions without permitting an expansion or contraction beyond predetermined limits. Thus, the dimensions or size of the chamber formed between the inner and outer tubes may be maintained within a predetermined range to permit the heat exchange between the flue gases and a predetermined amount of combustion air flowing through the chamber or passage, the maintaining of a predetermined airflow thus assisting in preventing a local hot spot from increasing in temperature through a restriction of a passage or chamber.

Referring to FIG. 3 it can be seen that the hook-receiving elements 52 are attached to the interior of the outer shell and are positioned to register with and receive the hook elements 51 located on the exterior of the inner tube.

The embodiments of the recuperator illustrated herein has an inner shell 10 with a first or lower zone of a plurality of rows of hook spacers. with each spacer extending a predetermined distance out from the inner shell and the hooked portion of the spacer opening upwardly, a second or intermediate zone of a plurality of rows of hook spacers with each spacer extending further out from the inner shellthan those in the lower zone and also opening upwardly, and a third or top zone of a plurality of rows of hook spacers with each spacer extending further outwardly from the inner shell than the spacers in the second zone and having hook portions which open downwardly.

Each row of hook spacers in all three zones on the inner shell has the individual hook spacers positioned in staggered relationship around the circumference of the inner shell with respect to the individual hook spacers in adjacent rows.

The larger outer shell or tube 12 has a like plurality of rows of inwardly extending hook-receiving elements or U-shaped brackets 52 positioned to register with and receive the hooked portions of the hook elements 51 extending outwardly from the inner shell.

Assembly of the two shells together is accomplished by making the inner shell 10 in two sections. The outer shell 12 is slipped over the lower section of the inner shell, including the first and second zones, with the U-brackets 52 disposed circumferentially intermediate the hook spacers 51 to permit the unobstructed passage of the U-brackets between the hook spacers as the outer shell slides over the inner shell.

When the rows of U-brackets 52 reach a position just above their corresponding rows of hook spacers 51, the outer shell is rotated to bring each U-bracket directly above its corresponding hook spacer. The outer shell is then lowered farther bringing the upwardly opening hook portion of a spacer into a re gistering or hooked position with its corresponding U-bracket. The second section of the inner shell, including the third or upper zone or all of the hook spacers which open downwardly, is then lowered into the upper part of the outer shell. The hook spacers are disposed between the Ubrackets to permit the sliding entry.

When the rows of book spacers in the third zone reach a position just above their corresponding rows of U-brackets, the inner shell is rotated to bring each hook spacer directly above its corresponding U-bracket. The inner shell is then lowered farther, bringing the downwardly opening hook spacers into registration with the U-brackets. The two sections of the inner stack are then secured together as by welding to form the final assembly. The hook spacers open both downwardly and upwardly so that when they are in registration with their corresponding U-brackets, the outer shell is held in a unitary relationship with respect to the inner shell or tube. The dimensions of the hook spacers and the U-brackets permits sliding engagement, even though the two shells are still held in one assembly during expansion or contraction of the shells. The inner and normally hotter shell will have normally a greater dimensional change thanthe outer and normally cooler shell.

There has thus been described heat exchange apparatus which includes a first structural member and a second structural member subjected to varying temperatures and defining a passageway therebetween. Means are provided for maintaining the spacing between the first and second members within a predetermined range to control the size of the passageway and provide support from one member to the other. The spacing means includes a first element extending from the first member toward the second member and having a hook means formed thereon, and a second element extending from a second member toward the first member and having an opening formed therein to receive and restrain movement of the hook means in response to varying temperature conditions. While the apparatus has been described in connection with and has particularly advantageous usefulness with a metal recuperator, it should be kept in mind that the invention may be applicable to other heat exchange installations that are within the scope of the description herein.

There has been generically disclosed apparatus for providing heat exchange between a substance and a means adapted to supply heat to or remove heat from the substance which comprises a first structural member having a first surface adapted to be placed in heat exchange relationship with the heat removal-supplying means and a second surface adapted to be placed in heat exchange relationship with the substance;

l a second structural member coofiarating with the first structural member to form a chamber for receiving one of the substance or the heat removal-supplying means; and means for f maintaining the spacing between the first and second structural members within a predetermined range to control the size of the chamber and provide a supporting relationship between the structural members including a hook element extending from one of the structural members, and an associated hook-receiving element extending from the other of the strucftural members having an opening formed therein to receive and restrain or limit movement of the hook element. The

' f opening formed in the hook-receiving element may be elongated in any direction to permit a sliding engagement with said 2 I hook element to accommodate different amounts of contrac 1 tion and expansion of said structural members.

In conclusion, it is pointed out that while the illustrative examples constitute practical embodiments of the invention, it is not intended to limit the invention to the exact details shown fsince modifications may be made without departing from the spirit and scope of the invention disclosed.

I claim: I. A recuperator for providing a heat exchange between hot gases which may result from exhaust products from a comi bustion furnace and relatively cool gases which may be used to f supply combustion air to burners in the combustion furnace comprising an inner tube; means forming an air passage around said inner tube; and means for maintaining a predeter- 'mined spacing between said passage forming means and said inner tube including a first element extending into said "passage from one of said passage forming means and inner 'tube and having a hook means formed thereon, and a second .element extending into said passage from the other of said passage forming means and said inner tube and having an opening formed therein to receive and restrain movement of said hook means; a plurality of rows of pairs of first and I second elements being spaced from each other along said .inner tube; the hook means of a first element in a first of said rows opening in a first direction, the hook means of a first element in a second of said rows opening in a second direction to prevent disengagement of said hook means from said second element.

2. A recuperator as defined in claim 1 in which said first element comprises an elongate spacer bar attached to said inner surrounding said inner tube and defining a passage -.therebetween; and means for maintaining said inner and outer itubes in a predetermined spaced relationship comprising a plurality of hook elements attached to one of said inner and uter tubes and extending toward the other of said tubes in aid passage, and a like plurality of associated hook-receiving 1 elements attached to the other of said tubes and extending 'ward said one tube in said passage; each of said hook-receiving elements having an opening formed therein to receive and restrain movement of a corresponding hook element in a direction transverse to said passageway; said corresponding hook andhook-receiving elements being arranged in a plurality of rows, each row extending around said passageway; a hook element in a first of said rows opening in a first direction and a hook element in a second of said rows opening in a second direction to prevent disengagement of said hook elements from their hook-receiving elements. a

5. A recuperator as defined in claim; in which the passage between said inner and outer tubes is closed at one end by a transverse partition joining said tubes, ..and is closed at the other end of-said tubes by means including an expansion bellows; the closure of both'ends in cooperation with said hook and hook-receiving elements providing a unitary structure which can accommodate different expansions and contractions of said tubes both in the direction of and transverse to said passage.

6. A recuperator comprising an inner tube; an outer tube surrounding said inner tube and defining a passage therebetween; and means for maintaining said inner and outer tubes in a predetermined spaced relationship comprising a plurality of hook elements attached to one of said inner and outer tubes and extending toward the other of said tubes in said passage and a like plurality of associated hook-receiving elements attached to the other of said tubes and extending toward said one tube in said passage, each of said hook-receiving elements having an opening formed therein to receive and restrain movement of a corresponding hook element in a direction transverse to said passageway; said corresponding hook and hook-receiving elements being arranged in a plurality of rows, each row extending around said passageway; said plurality of rows being divided into a plurality of zones, the dimensions of one of said hook and hook-receiving elements of all the elements in a first zone being varied from the dimensions of one of said hook and hook-receiving elements of all the elements in a second zone to accommodate varying amounts of expansion and contraction between said first and second zones.

7. A recuperator as defined in claim 6, in which the hook and hook-receiving elements in one row are positioned in a staggered relationship aroundsaid passage with respect to the hook and hook-receiving elements in other rows to provide a distributed support relationship between said inner and outer tubes.

8. A recuperator as defined in claim 6 in which said hook elements are elongate bars having a flange extending vertically therefrom and in which said elongate bars are attached to said inner tube to reinforce said inner tube.

9. A recuperator as defined in claim 6 in which said hookreceiving elements are also hook-shaped.

10. A recuperator as defined in claim 6 in which the passage between said inner and outer tubes is closed at one end by a transverse partition joining said tubes and is closed at the other end by means including an expansion bellows to form in cooperation with said hook and hook-receiving elements a unitary structure which'can accommodate different expansions and contractions of said tubes both in the direction of and transverse to said passage. 

